Dynamic stabilization member with molded connection

ABSTRACT

A dynamic fixation medical implant having at least two bone anchors includes a longitudinal connecting member assembly having at least one transition portion and cooperating outer sleeve, both the transition portion and sleeve being disposed between the two bone anchors. The transition portion includes a rigid length or rod having apertures therein and a molded plastic length that extends through the apertures, thus attaching the plastic length to the rigid length. The sleeve surrounds the transition portion and extends between the pair of bone anchors, the sleeve being compressible in a longitudinal direction between the bone anchors.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/931,161, filed Jan. 26, 2011, now U.S. Pat. No. ______, which is aContinuation of U.S. patent application Ser. No. 12/008,067, filed Jan.8, 2008, now U.S. Pat. No. 7,901,437, that claimed the benefit of U.S.Provisional Application No. 60/897,723 filed Jan. 26, 2007, each ofwhich are incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention is directed to dynamic fixation assemblies for usein bone surgery, particularly spinal surgery, and in particular tolongitudinal connecting members for such assemblies, the connectingmembers being attached to at least two bone fasteners.

Historically, it has been common to fuse adjacent vertebrae that areplaced in fixed relation by the installation therealong of bone screwsor other bone anchors and cooperating longitudinal connecting members orother elongate members. Fusion results in the permanent immobilizationof one or more of the intervertebral joints. Because the anchoring ofbone screws, hooks and other types of anchors directly to a vertebra canresult in significant forces being placed on the vertebra, and suchforces may ultimately result in the loosening of the bone screw or otheranchor from the vertebra, fusion allows for the growth and developmentof a bone counterpart to the longitudinal connecting member that canmaintain the spine in the desired position even if the implantsultimately fail or are removed. Because fusion has been a desiredcomponent of spinal stabilization procedures, longitudinal connectingmembers have been designed that are of a material, size and shape tolargely resist flexure, extension, torsion, distraction and compression,and thus substantially immobilize the portion of the spine that is to befused. Thus, longitudinal connecting members are typically uniform alongan entire length thereof, and usually made from a single or integralpiece of material having a uniform diameter or width of a size toprovide substantially rigid support in all planes.

Fusion, however, is not always desirable. An alternative to fusion andthe use of more rigid longitudinal connecting members or other rigidstructure has been a “soft” or “dynamic” stabilization approach in whicha flexible loop-, S-, C- or U-shaped member or a coil-like and/or aspring-like member is utilized as an elastic longitudinal connectingmember fixed between a pair of pedicle screws in an attempt to create,as much as possible, a normal loading pattern between the vertebrae inflexion, extension, distraction, compression, side bending and torsion.Another type of soft or dynamic system known in the art includes boneanchors connected by flexible cords or strands, typically made from aplastic material. Such a cord or strand may be threaded throughcannulated spacers that are disposed between adjacent bone anchors whensuch a cord or strand is implanted, tensioned and attached to the boneanchors. The spacers typically span the distance between bone anchors,providing limits on the bending movement of the cord or strand and thusstrengthening and supporting the overall system. Such cord orstrand-type systems require specialized bone anchors and tooling fortensioning and holding the chord or strand in the bone anchors. Althoughflexible, the cords or strands utilized in such systems do not allow forelastic distraction or stretchability of the system once implantedbecause the cord or strand must be stretched or pulled to maximumtension in order to provide a stable, supportive system.

The complex dynamic conditions associated with spinal movement make it achallenge to design flexible and/or elastic elongate longitudinalconnecting members that exhibit an adequate fatigue strength to providestabilization and protected motion of the spine, without fusion, andallow for some natural movement of the portion of the spine beingreinforced and supported by the elongate elastic or flexible connectingmember. A further challenge are situations in which a portion or lengthof the spine requires a more rigid stabilization, possibly includingfusion, while another portion or length may be better supported by amore dynamic system that allows for protected movement.

SUMMARY OF THE INVENTION

Longitudinal connecting member assemblies according to the invention foruse between at least two bone anchors provide dynamic, protected motionof the spine and may be extended to provide additional dynamic sectionsor more rigid support along an adjacent length of the spine, withfusion, if desired. According to the invention, an elongate moldedplastic structure, such as an elastomer is fixed to an end portion of anelongate rigid portion by molding or other fixing processes, including,but not limited to chemical bonding, blending, or surface adherence. Forexample, in an embodiment of the invention, molded plastic is disposedwithin a plurality of through bores of the end portion of a rigid rod. Alongitudinal connecting member assembly according to the invention thusincludes a transition or connection portion that is placed between apair of bone anchors, the transition portion having a firstsubstantially solid rigid portion and a second molded portion having atleast some elasticity. A sleeve or spacer surrounds the juncture of thefirst and second portions at the transition portion. The sleeve extendsbetween the pair of bone anchors and is in contact therewith. Thetransition portion and the outer sleeve cooperate dynamically, bothfeatures having some flexibility, with the outer sleeve primarilyprotecting and limiting flexing movement of the inner transitionportion. The outer sleeve may include a grooved portion that may becompressed upon installation between two bone anchors.

Embodiments according to the invention, include, for example, asubstantially solid rigid first portion, such as a metal rod having aplurality of apertures formed near an end thereof. A second solidelastic rod portion is fabricated by a molding process wherein theelastic rod portion is formed adjacent the metal rod portion such thatthe plastic polymer forming the elastic rod portion also flows into theapertures of the metal rod thereby fixing the first and second portionsto one another.

A variety of embodiments according to the invention are possible. Forexample, cylindrical rods, bars of square or rectangular cross-section,or other substantially rigid structures having different measures ofrigidity may be connected with flexible rods or bars of varyingstiffness and elasticity according to embodiments of the invention.Either rigid portions or flexible portions may be of greater or lesserlengths for attaching to one or up to a plurality of bone anchors.

OBJECTS AND ADVANTAGES OF THE INVENTION

Therefore, it is an object of the present invention to provide dynamicmedical implant stabilization assemblies having longitudinal connectingmembers that include both rigid and more flexible sections or lengths,the flexible sections allowing for at least one of bending, torsion,compression and distraction of the assembly. Another object of theinvention is to provide such an assembly wherein the flexible section orsections are insertable into a protective outer sleeve. A further objectof the invention is to provide such an assembly wherein the outer sleevemay be compressed upon installation. A further object of the inventionis to provide dynamic medical implant longitudinal connecting membersthat may be utilized with a variety of bone screws, hooks and other boneanchors. Another object of the invention is to provide a more rigid orsolid connecting member portion or segment, if desired, such as a solidrod portion integrally linked to one or more flexible portions orsegments. Additionally, it is an object of the invention to provide alightweight, reduced volume, low profile assembly including at least twobone anchors and a longitudinal connecting member therebetween.Furthermore, it is an object of the invention to provide apparatus andmethods that are easy to use and especially adapted for the intended usethereof and wherein the apparatus are comparatively inexpensive to makeand suitable for use.

Other objects and advantages of this invention will become apparent fromthe following description taken in conjunction with the accompanyingdrawings wherein are set forth, by way of illustration and example,certain embodiments of this invention.

The drawings constitute a part of this specification and includeexemplary embodiments of the present invention and illustrate variousobjects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged and partial exploded perspective view of apolyaxial bone screw and cooperating dynamic longitudinal connectingmember according to the invention (shown without the sleeve of FIG. 5).

FIG. 2 is an enlarged and partial exploded front elevational view of thedynamic longitudinal connecting member of FIG. 1.

FIG. 3 is an enlarged and partial front elevational view of the dynamiclongitudinal connecting member of FIG. 1.

FIG. 4 is a cross-sectional view taken along the line 4-4 of FIG. 3.

FIG. 5 is an enlarged front elevational view of the sleeve or spacer forthe dynamic longitudinal connecting member of FIG. 1.

FIG. 6 is a top plan view of the spacer of FIG. 5.

FIG. 7 is a side elevational view of the spacer of FIG. 5.

FIG. 8 is an enlarged and partial front elevational view of thelongitudinal connecting member of FIG. 1, the spacer of FIG. 5 and shownwith two polyaxial bone screws of FIG. 1, with portions broken away toshow the detail thereof.

FIG. 9 is an enlarged front elevational view a second embodiment of adynamic longitudinal connecting member according to the invention shownassembled with a fixed open screw and a fixed closed screw.

FIG. 10 is a rear elevational view of the assembly of FIG. 9 withportions broken away to show the detail thereof.

FIG. 11 is a top plan view of the assembly of FIG. 9 with portionsbroken away to show the detail thereof.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which may be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed structure. It is also noted that any reference tothe words top, bottom, up and down, and the like, in this applicationrefers to the alignment shown in the various drawings, as well as thenormal connotations applied to such devices, and is not intended torestrict positioning of the connecting member assemblies of theapplication and cooperating bone anchors in actual use.

With reference to FIGS. 1-8, the reference numeral 1 generallydesignates a dynamic stabilization longitudinal connecting memberassembly according to the present invention. The connecting memberassembly 1 is elongate, having a central axis A and generally includes afirst rigid member 6, a second more flexible, elastomeric member 7 and acentral, dynamic connection or transition portion or segment 8 disposedat and near a juncture of the members 6 and 7. The transition portion orsegment 8 is receivable in a spacer or sleeve 10 with the sleeve 10ultimately in position about the segment 8 when the assembly 1 isoperatively assembled with at least a pair of bone screw assemblies 15as illustrated in FIG. 8. The bone screw assembly, generally 15, thatmay be used with longitudinal connecting member assemblies 1 of theinvention is also illustrated in FIG. 1.

The rigid member 6 is typically a substantially solid structure, such asthe illustrated solid rod having an outer cylindrical surface 20. Therigid member 6 further includes an end 22 that is hollowed out and/orincludes a plurality of through bores or apertures. In the illustratedembodiment, a rod portion 24 adjacent to the end 22 is substantiallytubular, having an inner cylindrical surface 26 and a plurality ofthrough apertures or through bores 28 running through and being open atboth the outer surface 20 and the inner surface 26.

The elastomeric member 7 in the illustrated embodiment is substantiallybar-shaped, having an elongate portion 30 with a substantially squarecross-section, a tapered portion 32 and a rigid member connectionportion 34. The connection portion 34 is disposed near an end 36 of themember 7. As illustrated in FIG. 4, the elongate portion 30 has a widthmeasured at the cross-section that is substantially the same as adiameter of the cylindrical member 6, with the tapered portion 32gradually providing the minor transition in shape from the bar shape ofthe elongate portion 30 of the member 7 to the cylindrical shape of theportion 24 of the member 6. The portions 30, 32 and 34 are integral andpreferably fabricated by molding the member 7 in the presence of andadjacent to the rigid member 6 so that the portion 34 flows into a voiddefined by the inner cylindrical surface 26 as the portions 30 and 32are also molded, with the portion 34 further flowing through each of theapertures 28 of the rigid member 6. It is also foreseen that in certainembodiments, the portion 34 may be fabricated separately from the rigidmember 6 with flexible protrusions 40 of the portion 34 being sized andshaped (such as by separate mold or machining) for being received withinthe apertures 28 of the rigid member 6 when the end 36 of theelastomeric member 7 is inserted into the rigid member 6 at the end 22.

It is foreseen that each of the members 6 and 7 may be cylindrical inshape as illustrated in the embodiment shown in FIGS. 9-11. It is alsoforeseen that one or both of the members 6 and 7 may have other forms,including but not limited to oval, square and rectangular cross-sectionsas well as other curved or polygonal shapes, the members 6 and 7 havingthe same or different cross-sections. The members 6 and 7 are each of alength for cooperating with at least one and up to a plurality of boneattachment members, such as bone screws 15, other bone screws as will bedescribed below, or hooks. The rigid member 6 is made from metal, metalalloys or other suitable materials, including plastic polymers such aspolyetheretherketone (PEEK), ultra-high-molecular weight-polyethylene(UHMWP), polyurethanes and composites. The elastomeric member 7 is madefrom natural or synthetic elastomers, including, but not limited topolyisoprene (natural rubber), and synthetic polymers, copolymers, andthermoplastic elastomers, and mixtures thereof, with the illustratedmember 7 being a polyurethane elastomer. The illustrated sleeve 10 isalso preferably made from a plastic, such as a thermoplastic elastomer,for example, polyethylene or polycarbonate-urethane having a greaterstiffness than the elastomer of the member 7. In order to have low or nowear debris, the sleeve 10 inner surfaces and/or outer surfaces ofcooperating portions of members 6 and 7 may be coated with an ultrathin, ultra hard, ultra slick and ultra smooth coating, such as may beobtained from ion bonding techniques and/or other gas or chemicaltreatments. It is foreseen that the member 7 may be sized and made fromsuch materials as to provide for a relatively more rigid assembly 1 or arelatively more flexible assembly 1 with respect to flex or bendabilityalong the transition portion 8 and the portion 30. Furthermore, when theportion 30 is elongate, sleeves 10 are preferably disposed between bonescrews along such length. Also, since the distance between the bonescrews can vary, the member 7 may need to be more or less stiff.

With particular reference to FIGS. 5-8, the sleeve or spacer 10 is apart of the assembly 1 that advantageously cooperates with the midsection or transition portion 8 of the assembly 1, providing limitationand protection of movement of the section 8. The sleeve 10 also protectspatient body tissue from damage that might otherwise occur in thevicinity of the juncture of the rigid member 6 and elastomeric member 7.Thus, the sleeve 10 is sized and shaped for substantially even andprecise alignment and substantial contact between flat end faces 46 and48 of the sleeve 10 and cooperating flat side surfaces of the bonescrews 15 as will be described in greater detail below. Furthermore, aswill be discussed in greater detail below, in certain embodimentsaccording to the invention, when the sleeve 10 is implanted, and thebone screw assemblies 15 are tightened into a locked position withrespect to the longitudinal connecting member assembly 1, the toolsutilized to implant the assembly 1 and/or the bone screws 15 may bemanipulated so as to axially compress the sleeve 10 between facingsurfaces of adjacent bone screws 15. Such compression duringinstallation results in some tension and/or distraction of the member 7located between the bone screws 15 when the implantation tools areremoved from the bone screws 15, as the sleeve surfaces 46 and 48 thenpress against the facing bone screw surfaces, but the connection portion8 is otherwise fixed with respect to each of the bone screws 15. Suchdynamic tension/compression relationship between the sleeve 10 and thecentral connection portion 8 provides further strength and stability tothe overall assembly and also allows for the entire connecting memberassembly 1 disposed between the bone screws 15 to elongate, if needed,in response to spinal movement. The increased stability and strength ofthe assembly advantageously allows for use of a smaller, more compact,reduced volume, lower profile longitudinal connecting member assembly 1and cooperating bone anchors than, for example, flexible cord and spacertype longitudinal connecting member assemblies.

The illustrated sleeve 10 has an outer rectangular cross-section withopposed sides or side surfaces 50 and a pair of opposedanterior/posterior sides or surfaces 52. Each of the surfaces 50, 52extend between the flat end faces 46 and 48. The geometry of the sleeve10 allows for a narrower width between the parallel surfaces 50 than adistance between the surfaces 52. Such geometry provides adequatestiffness or support for the flexible member 7 at the segment 8 inflexing due to the greater distance between the posterior/anteriorcurved surfaces 52, while the more narrow width or distance between theflat surfaces 50 allows for placement of the sleeve 10 between adjacentvertebrae without engagement with such vertebrae. Stated in another way,a cylindrical sleeve having a diameter large enough to produce a desiredlimit of bending or flexing movement of the member 7 at the central ortransition portion 8 would most likely have a diameter large enough toresult in interference of the sleeve cylindrical surface with portionsof adjacent vertebrae. The rectangular cross-section of the sleeve 10allows allow for adequate clearance but do not detract from an overallstrength of the sleeve 10.

Extending along a substantially central axis B of the sleeve 10 (thatcorresponds to the axis A when the transition portion 8 is disposed inthe sleeve 10) is an internal channel or bore 56 of substantially squarecross-section. The surfaces 58 defining the bore 56 are sized and shapedto slidingly receive the members 6 and 7, with chamfers 60 located atcorners defining the bore 56 to provide ease in receiving the member 7that has a square cross-section. The bore 56 is slightly greater in sizethan the member 7, allowing for axially directed sliding movement of thesleeve 10 with respect to the member 7 during installation of thetransition portion 8 into the sleeve 10 and also when both the portion 8and the sleeve 10 are implanted with the sleeve 10 located betweenadjacent bone screws 15.

In the illustrated embodiment, the sleeve 10 further includes aplurality of compression grooves 62. Sleeves 10 according to theinvention may include one, none or any desired number of grooves 62.Each groove 62 extends substantially uniformly about the sleeve 10 asillustrated in FIG. 7, being formed in the pairs of external surfaces50, 52 of the sleeve 10. The groove or grooves 62 may be added asdesired to advantageously increase a longitudinal compressibility of thesleeve 10 during installation between a pair of bone screws 15.

When the sleeve 10 is received about the central connection portion 8,the sleeve 10 completely surrounds the central portion 8 as illustratedin FIG. 8. It is noted that in addition to limiting the bendability ofthe central connection portion 8 and thus providing strength andstability to the assembly 1, the sleeve 10 also keeps scar tissue fromgrowing into the portion 8 at the end 22 and apertures 28, thuseliminating the need for a sheath-like structure to be placed, adheredor otherwise applied to the central connection portion 8.

The dynamic connecting member assembly 1 cooperates with at least a pairof bone anchors, such as the polyaxial bone screws, generally 15 andcooperating closure structures 65 shown in FIG. 1, the assembly 1 beingcaptured and fixed in place at the portions 6 and 7 by cooperationbetween the bone screws 15 and the closure structures 65. The sleeve 10is sized and shaped to closely fit between pairs of bone screws 15 orother bone anchors or implants, cooperating with the central connectionportion 8 to support adjacent vertebrae.

Because the members 6 and 7 are both solid and, as illustrated, eithersubstantially cylindrical (member 6) or of other uniform cross-section(member 7), the connecting member assembly 1 may be used with a widevariety of bone anchors already available for cooperation with rigidrods including fixed, monoaxial bone screws, hinged bone screws,polyaxial bone screws, and bone hooks and the like, with or withoutcompression inserts, that may in turn cooperate with a variety ofclosure structures having threads, flanges, or other structure forfixing the closure structure to the bone anchor, and may include otherfeatures, for example, break-off tops and inner set screws. The boneanchors, closure structures and the connecting member assembly 1 arethen operably incorporated in an overall spinal implant system forcorrecting degenerative conditions, deformities, injuries, or defects tothe spinal column of a patient.

The solid portions 6 and 7 are particularly suited for use withpolyaxial bone screws. For example, a spline capture connectionpolyaxial bone screw as described in U.S. Pat. No. 6,716,214 andincorporated by reference herein, may be used with longitudinalconnecting member assemblies according to the invention.

The illustrated polyaxial bone screw 15 is particularly advantageous foruse with assemblies according to the invention as the screw 15 includesa squared off seat and compression member combination that securelyreceives both cylindrical and bar-shaped longitudinal connectingmembers. With reference to FIGS. 1 and 8, the illustrated polyaxial bonescrew assembly 15 includes a shank 74 that further includes a body 76integral with an upper portion or capture structure 78; a receiver 80;and an independent retainer illustrated as an open collar-like retainingand articulating structure 82 and a compression member 84. The shank 74,the receiver 80, the retainer 82 and the compression member 84preferably are assembled prior to implantation of the shank body 76 intoa vertebra (not shown).

FIG. 1 further shows the closure structure 65 for compressing andbiasing the longitudinal connecting member portion 6 or the portion 7against the compression member 84 which presses against the shank upperportion 78 which biases the retainer 82 into fixed frictional contactwith both the shank upper portion 78 and the receiver 80, so as to fixthe portion 6 or the portion 7 relative to the vertebra (not shown). Thereceiver 80, the retainer 82 and the shank 74 cooperate in such a mannerthat the receiver 80 and the shank 74 can be secured at any of aplurality of angles, articulations or rotational alignments relative toone another and within a selected range of angles both from side to sideand from front to rear, to enable flexible or articulated engagement ofthe receiver 80 with the shank 74 until both are locked or fixedrelative to each other near an end of an implantation procedure.

The shank 74, best illustrated in FIGS. 1 and 5, is elongate, with theshank body 76 having a helically wound bone implantable thread 85extending from near a neck 86 located adjacent to the upper portion 78to a tip 88 of the body 76 and extending radially outwardly therefrom.During use, the body 76 utilizing the thread 85 for gripping andadvancement is implanted into a vertebra (not shown) leading with thetip 88 and driven down into the vertebra with an installation or drivingtool (not shown), so as to be implanted in the vertebra to near the neck86. The shank 74 has an elongate axis of rotation generally identifiedby the reference letter C.

The neck 86 extends axially upwardly from the shank body 76. Furtherextending axially from the neck 86 is the shank upper portion or capturestructure 78 that provides a connective or capture apparatus disposed ata distance from the thread 85 and thus at a distance from the vertebra(not shown) when the body 76 is implanted in such vertebra.

The shank upper portion 78 is configured for connecting the shank 74 tothe receiver 80 and capturing the shank 74 in the receiver 80. The shankupper portion 78 has an outer, convex and substantially sphericalsurface 90 that extends outwardly and upwardly from the neck 86 andterminates at a curved top 92. The spherical surface 90 has an outerradius configured for sliding cooperation and ultimate frictional matingwith a concave surface of the retainer 82 having a substantially similarradius. The spherical surface 90 is smooth, but it is foreseen that suchsurface may include a roughened or textured surface or surface finish,or may be scored, knurled, or the like, for enhancing frictionalengagement with the retainer 82. A counter sunk drive feature 94 isformed in the top 92 (shown as a hexagonal aperture). In operation, adriving tool (not shown) engages the feature 94 for driving the shankbody 76 into bone. The drive feature 94 may take a variety oftool-engaging forms and may include one or more apertures or imprints ofvarious shapes, such as a pair of spaced apart apertures or amulti-lobular aperture, such as those sold under the trademark TORX, orthe like. It is foreseen that in some embodiments, the bone screw shankupper portion may have an external tool engagement structure.

The illustrated shank 74 is cannulated, having a small central bore 95extending an entire length of the shank 74 along the axis C, coaxialwith the threaded body 76. The bore 95 has a first circular opening atthe shank tip 88 and a second circular opening at the drive feature 94.The bore 95 provides a passage through the shank 74 interior for alength of wire (not shown) inserted into a vertebra (not shown) prior tothe insertion of the shank body 76, the wire providing a guide forinsertion of the shank body 76 into the vertebra.

To provide a biologically active interface with the bone, the threadedshank body 76 may be coated, perforated, made porous or otherwisetreated. The treatment may include, but is not limited to a plasma spraycoating or other type of coating of a metal or, for example, a calciumphosphate; or a roughening, perforation or indentation in the shanksurface, such as by sputtering, sand blasting or acid etching, thatallows for bony ingrowth or ongrowth. Certain metal coatings act as ascaffold for bone ingrowth.

Bio-ceramic calcium phosphate coatings include, but are not limited to:alpha-tri-calcium phosphate and beta-tri-calcium phosphate (Ca₃(PO₄)₂,tetra-calcium phosphate (Ca₄P₂O₉), amorphous calcium phosphate andhydroxyapatite (Ca₁₀(PO₄)₆(OH)₂). Coating with hydroxyapatite, forexample, is desirable as hydroxyapatite is chemically similar to bonewith respect to mineral content and has been identified as beingbioactive and thus not only supportive of bone ingrowth, but activelytaking part in bone bonding.

The receiver 80 has a generally squared-off U-shaped appearance with adiscontinuous partially cylindrical inner profile and a faceted outerprofile. The receiver 80 includes a base 102 integral with a pair ofupstanding arms 104 forming a cradle and defining a squared-off U-shapedchannel 106 between the arms 104 with an upper opening 107 and a lowerseat 108 having a width for receiving the bar-shaped portion 30 of theelastomeric member 7 or the rigid rod portion 6, for operably snuglyreceiving either of the members 6 and 7.

Each of the arms 104 has an interior surface 110 that defines the innercylindrical profile and includes a partial helically wound guide andadvancement structure 112. In the illustrated embodiment, the guide andadvancement structure 112 is a partial helically wound interlockingflangeform configured to mate under rotation with a similar structure onthe closure structure 65, as described more fully below. However, it isforeseen that the guide and advancement structure 112 couldalternatively be a square-shaped thread, a buttress thread, a reverseangle thread or other thread like or non-thread like helically wounddiscontinuous advancement structure for operably guiding under rotationand advancing the closure structure 65 downward between the arms 104, aswell as eventual torquing when the closure structure 65 abuts againstthe rigid rod portion 6 or the elastomeric bar 7.

Tool engaging apertures 114 are formed on or through surfaces of thearms 104 that may be used for holding the receiver 80 during assemblywith the shank 74, the retainer 82 and the compression member 84 andalso during the implantation of the shank body 76 into a vertebra (notshown). Furthermore, each of the arms 104 also includes a V-shaped orundercut tool engagement groove 116, formed on outer surfaces thereofwhich may be used for holding the receiver 80 with a holding tool (notshown) having projections that are received within the grooves 116during implantation of the shank body 76 and/or during subsequentinstallation of the longitudinal connecting member assembly 1 and theclosure structure 65. It is foreseen that tool receiving grooves orapertures may be configured in a variety of shapes and sizes and bedisposed at other locations on the receiver arms 104.

On either side of the channel 106, the arms 104 of the receiver 80include opposed planar surfaces 120 that cooperate with the opposed flatsurfaces 46 and 48 of the sleeve 10 when the assembly 1 is operativelyattached to the bone screws 15 as illustrated in FIG. 8. With referenceto FIG. 1, communicating with and located beneath the channel 106 of thereceiver 80 is a chamber or cavity 122 substantially defined by apartial inner spherical seating surface 124 of the base 102. The seatingsurface 124 is sized and shaped for slidable mating and eventualfrictional engagement with the retainer 82, as described more fullybelow. The cavity 122 opens upwardly into the U-shaped channel 106 anddownwardly to a bore 126 defined by a neck 128 that opens to a lowerexterior 130 of the base 102. The bore 126 is coaxially aligned withrespect to a rotational axis D of the receiver 80. The neck 128 and theassociated bore 126 are sized and shaped to be smaller than an outerradial dimension of the open, uncompressed retainer 82, as will bediscussed further below, so as to form a restriction at the location ofthe neck 128 relative to the retainer 82, to prevent the uncompressedretainer 82 from passing from the cavity 122 and out to the lowerexterior 130 of the receiver 80 when the retainer 82 is seated andloaded.

The partially spherical and discontinuous or open retainer 82 that bothretains and articulates is used to hold the spherically surfaced 90upper portion 78 of the shank 74 within the receiver 80 and is alsoindependently slidably and pivotally engageable with both the shankupper portion 78 at the surface 90 and the receiver 80 at the seatingsurface 124. The retainer 82 illustrated in FIGS. 1 and 8 has anoperational central axis E that may be the same or different from theaxis C associated with the shank 74, or the axis D associated with thereceiver 80 when the shank upper portion 78 and the retainer 82 areinstalled within the receiver 80. The retainer 82 has a central channelor bore substantially defined by a discontinuous inner partiallyspherical surface 140 disposed between a top surface 142 and a bottomsurface 144 of the retainer 82. The inner spherical surface 140 has aradius sized and shaped to cooperate with a radius of the substantiallyspherical surface 90 of the shank upper portion 78 such that the surface140 slidingly and pivotally mates with the spherical surface 90. Thesurface 140 may include a roughening or surface finish to aid infrictional contact between the surface 140 and the surface 90, once adesired angle of articulation of the shank 74 with respect to theretainer 82 is reached.

The resilient retainer 82 includes first and second end surfaces, 146and 147 disposed in spaced relation to one another and a discontinuousouter partially spherically shaped surface 150. Both end surfaces 146and 147 are disposed substantially perpendicular to the top surface 142and the bottom surface 144. A width of the space between the surfaces146 and 147 is determined to provide adequate space for the retainer 82to be pinched, with the surfaces 146 and 147 compressed toward oneanother to an almost touching or touching configuration, to an extentthat the compressed retainer 82 is up or bottom loadable into thereceiver cavity 122 through the bore 126 defined by the restrictive neck128 while mounted on the neck 86 of the bone screw shank body 76. Afterpassing through the bore 126 simultaneously with the shank upper portion78, the retainer 82 expands or springs back to an original uncompressed,rounded or collar-like configuration of FIG. 1 once in the cavity 122.Once the resilient structure 82 returns to an original form, but nowsurrounding the spherical structure 78, the engaged structures 78 and 82are then movable together within the cavity 122 to a variety ofpositions in which the surface 150 of the structure 82 is in slidablemating engagement with the seating surface 124 of the receiver 80.

The embodiment shown in FIGS. 1 and 8 illustrates the surfaces 146 and147 as substantially parallel and vertical, however, it is foreseen thatit may be desirable to orient the surfaces obliquely or at a slightangle depending upon the amount of compression desired during loading ofthe retainer 82 into the receiver 80. Also, other embodiments accordingto the invention, particularly smaller bone screw assemblies, mayinclude retainers small enough to top load into the receiver channelupper opening 107, rather than loading through the receiver neck 128.

The compression member 84 is sized and shaped to be received by anduploaded into the receiver 80 at the neck 128. In operation, the member84 is disposed between the rigid member 6 or the elastomeric member 7and the upper portion 78 of the bone screw 74 as illustrated in FIG. 8.When the closure structure 65 presses upon the member 6 or the member 7,the member 6 or 7 operatively presses upon the compression member 84that in turn presses upon the shank upper portion 78 that in turnpresses against the retainer 82 that in turn presses against the seatingsurface 124 of the receiver 80, resulting in ultimate frictionalengagement and locking the angular position of the bone screw shank 74with respect to the receiver 80. The compression member 84 has anoperational central axis F that is the same as the central axis D of thereceiver 80. The compression member 84 has a central channel or throughbore substantially defined by a an inner cylindrical surface 160 and aninner partially spherical surface 162 (shown in phantom in FIG. 8). Thecompression member through bore is sized and shaped to receive a drivingtool (not shown) therethrough that engages the shank drive feature 94when the shank is driven into bone. The surface 162 is sized and shapedto cooperate with the spherical surface 90 of the shank upper portion 78such that the surface 162 slidingly and pivotally mates with thespherical surface 90. The surface 162 may include a roughening orsurface finish to aid in frictional contact between the surface 162 andthe surface 90, once a desired angle of articulation of the shank 74with respect to the retainer 12 is reached.

The compression member 84 also includes a substantially planar topsurface 164, a bottom surface 166 and an outer cylindrical surface 168.The cylindrical surface 168 is sized to be received within the interiorcylindrical surface 110 defining the receiver 80 at the arms 104 andlocated between the guide and advancement structure 112 and the chamber122 as best shown in FIG. 8. Thus, the compression member 84 ultimatelyseats on the shank upper portion 78 and is disposed at least partiallyin the channel 106 such that the compression member 84 top surface 164substantially contacts the member 6 or the member 7 when thelongitudinal connecting member assembly 1 is placed in the receiver 80and the closure structure 65 is tightened therein.

With reference to FIGS. 1 and 8, the closure structure or closure top 65can be any of a variety of different types of closure structures for usein conjunction with the present invention with suitable mating structureon the upstanding arms 104. In the embodiment shown, the closure top 65is rotatably received between the spaced arms 104, but could be aslide-in closure structure. The illustrated closure structure 65 issubstantially cylindrical and includes an outer helically wound guideand advancement structure 172 in the form of a flange form that operablyjoins with the guide and advancement structure 112 disposed on the arms104 of the receiver 80. The flange form utilized in accordance with thepresent invention may take a variety of forms, including those describedin Applicant's U.S. Pat. No. 6,726,689, which is incorporated herein byreference. It is also foreseen that according to the invention theclosure structure guide and advancement structure could alternatively bea buttress thread, a square thread, a reverse angle thread or otherthread like or non-thread like helically wound advancement structure foroperably guiding under rotation and advancing the closure structure 65downward between the arms 104 and having such a nature as to resistsplaying of the arms 104 when the closure structure 65 is advanced intothe U-shaped channel 106. The illustrated closure structure 65 alsoincludes a top surface 174 with an internal drive 176 in the form of anaperture that may be a hex drive, a star-shaped internal drive, forexample, sold under the trademark TORX or other internal drives such asslotted, tri-wing, spanner, two or more apertures of various shapes, andthe like. A driving tool (not shown) sized and shaped for engagementwith the internal drive 176 is used for both rotatable engagement and,if needed, disengagement of the closure 65 from the arms 104. It is alsoforeseen that the closure structure 65 may alternatively include abreak-off head designed to allow such a head to break from a base of theclosure at a preselected torque, for example, 70 to 140 inch pounds.Such a closure structure would also include a base having an internaldrive to be used for closure removal. A bottom surface 178 of theclosure may be planar or include a point, points, a rim or rougheningfor engagement with the member 6 or the member 7 of the longitudinalconnecting member assembly 1.

Prior to the polyaxial bone screw assembly 15 being placed in useaccording to the invention, the retainer 82 is first inserted about theneck 86 of the shank body 76 by inserting the shank tip 88 into theretainer through bore defined by the inner surface 140 and feeding theshank body 76 therethrough until the retainer 82 is located at the neck86. Alternatively, in certain embodiments, the retainer 82 is placednear the neck 86 and the end surfaces 146 and 147 are pulled away fromone another and pressed against and about the neck 86 until the surfaces146 and 147 expand around the neck 86 and then spring back into a firstposition with the inner surface 140 disposed adjacent to the neck 86 andthe top surface 142 facing toward the spherical surface 90 of the shankupper portion 78.

The compression member 84 is up or bottom loaded into the receiver 80through the bore 126 with the top surface 164 facing the bore 126 andthe cylindrical surface 168 moved upwardly through the neck 128. Thecompression member 84 may be placed on the shank upper portion 78 withand the spherical surface 162 seated on the surface 90 of the shankupper portion 78 and then uploaded simultaneously with the shank upperportion 78 and the retainer 82. The upper portion 78 and the connectedstructure 82 are then simultaneously up or bottom-loaded into thereceiver cavity 122 by inserting the upper portion 78 through the neck128 and into the cavity 122 and manually compressing the retainer 82 bypinching the surfaces 146 and 147 toward one another and inserting theneck 86 and the compressed retainer 82 into the bore 126 of the receiver80. After the retainer 82 moves beyond the bore 126 and into the cavity122, the compressive force is removed and the retainer 82 resilientlysprings back and returns to the original ring-like or collar-likeorientation, capturing the shank upper portion 78 within the receiver80. Then, the shank body 76 is pulled downwardly away from the receiver80, forcing the retainer 82 to temporarily expand about the sphericalsurface 90 of the shank upper portion 78 with the end surfaces 146 and147 moving away from one another. Such an expansion of the retainer 82allows the spherical surface 90 to slide into the retainer 82 until theouter surface 90 of the shank upper portion 78 is in sliding pivotalcooperation with the inner surface 140 of the retainer 82. The retainer82 resiliently returns to the original ring-link orientation, with thespherical surface 140 capturing the shank upper portion 78 at thespherical surface 90, but allowing for pivotal, sliding movement orarticulation of the retainer 82 with respect to the shank upper portion78. Once the retainer 82 returns to the original orientation, both theconnected structures 78 and 82 drop down to a seated position with theretainer 82 independently slidable with respect to both the shank upperportion 78 and the receiver 80, forming a multi- or compoundarticulation or joint between the shank 74 and the receiver 80. Thecompression member 84 may then be pressed downwardly and into fullcontact with the surface 90. It is noted that the receiver 80 mayinclude an inner ledge, ridge or inwardly extending protrusion orprotrusions to ensure that the compression member 84 does not slip outof the upper opening of the receiver 80.

The compression member 84, the retainer 82 and the attached shank upperportion 78 may then be manipulated into a substantially coaxial positionin readiness for bone implantation. The assembly 15 is typically screwedinto a bone, such as a vertebra (not shown), by rotation of the shank 74using a driving tool (not shown) that operably drives and rotates theshank 74 by engagement thereof with the drive feature 94.

Typically, the receiver 80, the compression member 84, and the retainer82 are assembled on the shank 74 before inserting the shank body 76 intoa vertebra. However, in certain circumstances, such as when a small bonescrew is utilized and the retainer is top loadable, the shank body 76can be first partially implanted with the shank upper portion 78extending proud to allow assembly with the receiver 80, followed byassembly with a top loaded retainer 12 and a top loaded compressionmember 84. Then the shank body 76 can be further driven into thevertebra.

The vertebra (not shown) may be pre-drilled to minimize stressing thebone and have a guide wire (not shown) inserted to provide a guide forthe placement and angle of the shank 74 with respect to the vertebra. Afurther tap hole may be made using a tap with the guide wire as a guide.Then, the bone screw assembly 15 or the solitary shank 74, is threadedonto the guide wire utilizing the cannulation bore 95 by first threadingthe wire into the opening at the bottom 88 and then out of the topopening at the drive feature 94. The shank 74 is then driven into thevertebra using the wire as a placement guide. It is foreseen that thescrews 15 and the longitudinal connecting member assembly 1 can beinserted in a percutaneous or minimally invasive surgical manner.

The sleeve 10 is typically cut to size by the surgeon for closelyfitting between a pair of adjacent bone screw assemblies 15. Thelongitudinal connecting member assembly 1 that has been fabricated toinclude the rigid member 6 with the elastomeric member 7 molded theretois then assembled with the sleeve 10 by inserting an end of either themember 6 or the member 7 into the bore 56 defined by the inner surfaces58 of the outer sleeve 10. The sleeve 10 is moved into position over thecentral portion 8, thus covering the rod portion 24 and the member 7connection portion 34.

With reference to FIG. 8, the longitudinal connecting member assembly 1is eventually positioned in an open or percutaneous manner incooperation with the at least two bone screw assemblies 15 with thesleeve 10 disposed between the two bone screw receivers 80 and a portionof the member 6 within one receiver 80 and a portion of the member 7within the other receiver 80. A closure structure 65 is then insertedinto and advanced between the arms 104 of each of the bone screwassemblies 15. The closure structure 65 is rotated, using a tool engagedwith the inner drive 176 until a selected pressure is reached at whichpoint the members 6 and 7 are each urged toward, but not completelyseated on the lower seat 108. For example, about 80 to about 120 inchpounds pressure may be required for fixing each bone screw shank 74 withrespect to the receiver 80.

As each closure structure 65 rotates and moves downwardly into therespective receiver 80, the bottom surface 178 presses against thelongitudinal connecting member assembly member 6 or 7 and the structure65 biases the member 6 or 7 downward into engagement with thecompression member 84 that operably produces a frictional engagementbetween the member 84 and the shank surface 90 and also urges the shankupper portion 78 toward the retainer 82 and, in turn, the structure 82toward the base 102 of the receiver 80, so as to frictionally seat thespherical surface 90 against the inner spherical surface 140 of theretainer 82 and the outer spherical surface 150 of the retainer 82against the internal spherical seating surface 124 of the receiver 80,also fixing the shank 74 and the retainer 82 in a selected, rigidposition relative to the receiver 80. At this time it is also possiblefor the retainer 82 to expand somewhat for an even tighter fit in thereceiver cavity 122.

It is foreseen that an assembly 1 according to the invention maycooperate with an open receiver that is integral or fixed in positionwith respect to a bone screw shank or bone hook, or with a receiverhaving limited angular movement with respect to the shank, such as ahinged connection, also with or without other compression members orinserts for fixing the assembly 1, the receiver and/or the bone anchorin a desired position or orientation with respect to the cooperatingvertebrae.

As indicated previously herein, as the closure structures 65 are rotatedand then tightened against the members 6 and 7 within a pair of spacedbone screw receivers 80, such bone screw receivers 80 may be tilted orotherwise pressed toward one another, thereby compressing the sleeve 10.When the insertion and tightening tools are removed, the sleeve 10,pressing against facing surfaces 120 of the cooperating bone screwreceivers 80, stretches and tensions the elastomeric member 7 that ispart of the transition portion 8 that is disposed between suchcooperating bone screw receivers 80. The assembly 1 is thussubstantially dynamically loaded and oriented relative to thecooperating vertebra, providing relief (e.g., shock absorption) andprotected movement with respect to flexion, extension, distraction andcompressive forces placed on the assembly 1 and the two connected bonescrews 15. The member 7 also allows the central portion 8 to twist orturn, providing relief for torsional stresses. The sleeve 10 limits suchtorsional movement as well as bending movement of the central connectionportion 8, providing spinal support. Furthermore, because the sleeve 10is compressed during installation, the sleeve advantageously allows forsome protected extension or distraction of both the central connectionportion 8 and the sleeve 10 as well as compression of the assembly 1 incooperation with the central connection portion 8.

If removal of the assembly 1 from any of the bone screw assemblies 15 isnecessary, or if it is desired to release the assembly 1 at a particularlocation, disassembly is accomplished by using the driving tool (notshown) that mates with the internal drive 176 on the closure structure65 to rotate and remove the closure structure 65 from the cooperatingreceiver 80. Disassembly is then accomplished in reverse order to theprocedure described previously herein for assembly.

Eventually, if the spine requires more rigid support, the connectingmember assembly 1 according to the invention may be removed and replacedwith another longitudinal connecting member, such as a solid rod, havingthe same diameter as the member 6 or a solid bar with the same width asthe member 7, utilizing the same receivers 80 and closure structures 65.Furthermore, it is noted that the members 6 and 7 may be elongate,allowing for connection of both rigid rod portions and/or elastomericportions of the assembly 1 with additional bone screws or other boneanchors along a patient's spine. A connecting member assembly accordingto the invention may also include more than one transition portion 8along a length thereof. Thus, such a connecting member may includevarious and alternating lengths of rigid and flexible support.

With reference to FIGS. 9-11, an alternative longitudinal connectingmember assembly embodiment according to the invention, generally 201includes a first rigid member 206, a second more flexible, elastomericmember 207 and a central, dynamic connection or transition portion orsegment 208 disposed at and near a juncture of the members 206 and 207.The transition portion or segment 208 is receivable in a spacer orsleeve 210 with the sleeve 210 ultimately in position about the segment208 when the assembly 201 is operatively assembled with at least a pairof bone screw assemblies 215 and 216 as illustrated in FIG. 8.Specifically, the connecting member assembly 201 is illustrated with thebone screw assembly 215 that is an open, monoaxial bone screw having afixed shank 217 and cooperating with a closure top 218 substantiallysimilar to the closure structure 65 previously described herein; andalso shown with the bone screw assembly 216 that is a closed monoaxialbone screw having a fixed shank 219 and cooperating with a set screw220.

The rigid member 206 is in the form of a rod identical or substantiallysimilar to the rigid member 6 previously described herein with respectto the assembly 1. Thus, the member 206 includes an apertured portion224 identical or substantially similar to the portion 24 previouslydescribed herein with respect to the rigid member 6. The elastomericmember 207 is substantially similar to the member 7 previously describedherein with respect to the assembly 1 with the exception that the member207 is in the form of a rod having substantially the same diameter asthe rod 206. Similar to the member 7, the member 207 is molded with aconnection portion 234 (similar to the portion 34 of the member 7) thatflows into the apertures of the rod portion 224 during fabrication ofthe longitudinal connecting member assembly 201. The sleeve or spacer210 is substantially similar to the spacer 10 previously describedherein with respect to the assembly 1 with the exception that the sleeve210 includes a central bore 256 having a circular cross-section thatslidingly receives the cylindrical members 206 and 207.

As with the assembly 1, and as illustrated in FIG. 9, the assembly 201readily cooperates with a wide variety of bone anchors and closures, andthus is not limited in use to the particular bone screws disclosedherein. In use, the longitudinal connecting member assembly 201 isfactory fabricated to provide the flexible central transition portion208. The sleeve 210 is slidable onto both the rigid portion 206 and theelastomeric portion 207, and placable about the central or transitionportion 208. The sleeve 210 (as well as the sleeve 10 previouslydescribed herein) my be cut to the precise desired size by the surgeon.The connecting member assembly 201 is eventually positioned in an openor percutaneous manner in cooperation with the bone screws 215 and 216with the sleeve 210 disposed between the two bone screws 216 and 217 andfitting closely therebetween. As with the assembly 1, closure structuresor screws 218 and 220 are inserted into the bone screws and the sleeve210 may be compressed by moving the bone screws 215 and 216 toward oneanother during tightening of the closure structures within the bonescrew receivers. When the insertion and tightening tools are removed,the sleeve 210, pressing against facing surfaces of the adjacentcooperating bone screw receivers, stretches and tensions the member 207that is part of the central connection portion 208. The assembly 201 isthus substantially dynamically loaded and oriented relative to thecooperating vertebra, providing relief (e.g., shock absorption) andprotected movement with respect to flexion, extension, distraction andcompressive forces placed on the assembly 201 and the two connected bonescrews 215 and 216. The elastomeric member 207 at the central portion208 allows the central portion 208 to twist or turn, providing relieffor torsional stresses. The sleeve 210 limits such torsional movement aswell as bending movement of the central connection/transition portion208, providing spinal support. Furthermore, because the sleeve 210 iscompressed during installation, the sleeve advantageously allows forsome protected extension or distraction of both the central connectionportion 208 and the sleeve 210 as well as compression of the assembly201 in cooperation with the central connection portion 208.

It is to be understood that while certain forms of the present inventionhave been illustrated and described herein, it is not to be limited tothe specific forms or arrangement of parts described and shown.

1-6. (canceled)
 7. In a medical implant assembly having at least twobone attachment structures cooperating with an elongate longitudinalconnecting member, the improvement wherein the connecting membercomprises: a) a transition portion at least partially disposed betweenthe bone attachment structures, the transition portion having i) a solidrigid rod having a solid outer surface with at least one opening in anend portion thereof, the rigid rod being attached to at least one of thebone attachment structures; and ii) a flexible member, a portion of themember disposed within the at least one opening, the flexible membercooperating with the bone attachment structures and being pre-tensioned;and b) an outer sleeve engaging and at least partially covering thetransition portion, the outer sleeve being positioned between the boneattachment structures and being under compression.
 8. In a medicalimplant assembly having at least two bone attachment structurescooperating with an elongate longitudinal connecting member, theimprovement wherein the connecting member comprises: a) a transitionportion at least partially disposed between the bone attachmentstructures, the transition portion having i) a solid rigid elongatesegment including a solid outer surface with at least one opening in anend portion thereof, the rigid segment being attached to at least one ofthe bone attachment structures; and ii) a flexible member, a portion ofthe member disposed within the at least one opening, the flexible membercooperating with the bone attachment structures to provide motiontherebetween and being pre-tensioned; and b) an outer sleeve engagingthe transition portion, the outer sleeve being positioned between thebone attachment structures and being under compression.